The goal of this research is to define the enzymatic mechanisms and the integrated metabolic processes that function to regulate and coordinate the dynamics of phospholipid metabolism during functional development of the rat lung. The characteristics and regulatory properties of choline kinase, choline phosphate: CTP cytidylyltransferase, diglyceride: CDP-choline, choline phosphotransferase, and phosphatidate phosphatase are investigated. Each is purified from both fetal and adult lung. Phosphatidate phosphatase -choline phosphotransferase coupled system is explored in detail. The competing reactions for diblyceride are evaluated in terms of their effect on the dynamics of diglyceride levels in microsomes. The dynamics of phosphatidylcholine synthesis and related metabolic pathways are studied with lung slice preparations. The pool sizes of choline phosphate, CDP-choline, CTP, CMP, glycerol-3-phosphate, dihydroxyacetone phosphate and lactate are measured in fetal and adult lung. The effects of various hormones on the above system are evaluated.